As is well known the human knee comprises an articulation of the femur, the tibia and the patella. The femur and the tibia are maintained in a condition of stable articulation by a number of ligaments of which the principal ones are the anterior and posterior cruciate ligaments and the lateral ligaments. The rupture of the anterior cruciate ligament is relatively commonly encountered as a result of sporting injury or the like. This rupture leads to knee instability and can be a debilitating injury.
There have been a number of procedures designed to reconstruct the anterior cruciate ligament. Initially, attempts were made to replace the anterior cruciate ligament with tendons harvested from elsewhere in the body. These tendons were connected respectively to the femur and the tibia by staples, screws or the like inserted exteriorly into the bone and forming an external attachment to which the tendon could be connected externally of the bone. In some cases, the tendon passed over the top of one of the femoral condyles before attachment to the femur and in other cases a hole was drilled through the femur from outside the bone into the intercondylar notch. These attempts at anterior cruciate ligament reconstruction had mixed success. The tendon tended to break at its point of connection to the bone, or become loose over time, indicating that the tendon bone interface was crucial for effective anterior cruciate ligament reconstruction.
These problems led to the use of bone-tendon-bone grafts generally harvested from mid-third patella tendon with a bone block at each end. Each bone block is inserted into an appropriate hole drilled in the femur or the tibia and secured in place by a screw driven between the wall of the hole and the bone block. While this system has been very successful in many respects a significant number of patients continue to have patella-femoral problems, especially over the mid-third patella tendon donor sites.
In an effort to overcome these problems it has been proposed to suture hamstring tendon to a bone block derived from coring the tibial tunnel and to thereby manufacture a bone/tendon/bone graft similar to a mid-third patella tendon graft. The present inventors have found that the bone quality is extremely variable. This results in poor fixation and poor intra-operative pull-out strength in some cases. This procedure was also found to be a very demanding surgical procedure, and therefore difficult to reproduce.
In all of these operations a hole is drilled into the femur in the region of the intercondylar notch to receive the replacement ligament. In order to ensure that the femoral end of the ligament is correctly placed the hole must be drilled laterally of the mid-line of the femoral notch and in a direction which is angled away from that mid-line. The hole itself extends anteriorly and laterally of the intercondylar notch. This means that, when looking from in front of a patient, the hole for a replacement ligament in the right knee extends into or through the left hand condyle and the hole for a replacement ligament in the left knee extends into or through the right hand condyle.
The present inventors have found that a conventional screw works acceptably in the left hand knee but not so well in the right hand knee. In the case of the right hand knee the present inventors have found that the ligament replacement, which should form a crescent at the back, ie. the posterior side, of the hole, tends to rotate in the hole moving forwardly as it is moved around the hole by the motion of the screw being driven into the hole. This rotation of the ligament has two deleterious consequences. Firstly, the movement of the ligament obscures the surgeons view of the head of the screw. This complicates the operation and means it is more likely that the screw will not be driven fully into the hole as is required for a successful operation. Secondly, the positioning of the ligament may not be correct leading to an increased likelihood of subsequent knee instability.